Information on Shearwater petrel

[Gareth J]

I am looking for some more information relating to the Shearwater Petrel.

A buddy I was diving with recently was using a Petrel.
Unusually, I was on OC, using an OSTC.

Both computers where running Buhlmann with the same GF settings. What confused me was her computer appeared to give longer stop times and the TTS was inaccurate.

I am unfamiliar with the Shearwater range and display's. However, I think I saw a sliding Stop Depth (as against a 3m incremental stops).
I am fully aware that most computers (and I assume the Shearwater), you can change the last stop depth. Obviously, if the last stop is at 3m (9ft), and you complete the last stop at 6m (18ft), the TTS will be inaccurate, as it is based on you moving too 3m.
However, I could swear that the ceiling was constantly moving, like the old 'dope on a rope' feature on the (very) old VR3's.

I would very much like to get a better understanding of the Petrel and how it behaves and the display, any information would be gratefully received.

Gareth

 

[Joneill]

Why not download the Petrel manual from the Sheawater website and see if that answers your questions?

 

[Vicko]

While they are both running Buhlman it's possible that they are running different implementations of it were the differences more then a minute or two apart?

 

[Gareth J]

I did have a quick look

Why not download the Petrel manual from the Sheawater website and see if that answers your questions?

I did have a quick look last night, and didn’t see what I was looking for. Although I was extremely tired having gotten in at 2:00 am after a very long drive.

 

[Gareth J]

While they are both running Buhlman it's possible that they are running different implementations of it were the differences more then a minute or two apart?

The difference was significant.

If we had exited the water on my computer we would have been inside the maximum dive time I put on the log before we entered the water. We significantly overran which is not looked on favourably in my group.
What was worse was the final TTS was significantly longer than that originally displayed on the Shearwater. (The stop was much longer). I can understand this if the final stop was set for 3m, we where at 6m. But it appeared as if the ceiling had moved to 1.0m when I was looking over her shoulder.
From what I remember, the display shown in the manual didn’t appear to match the manual. But that may be because all our dives where deco dives.

I don’t like overrunning the planned maximum time. I like to plan and manage the dive inside the plan. The shearwater fooled me on each dive and I would like to understand why.

I even did one day with another buddy mid way through where my dive was significantly deeper and longer.

Gareth

 

[GF99/99]

I am looking for some more information relating to the Shearwater Petrel.

A buddy I was diving with recently was using a Petrel.
Unusually, I was on OC, using an OSTC.

Both computers where running Buhlmann with the same GF settings. What confused me was her computer appeared to give longer stop times and the TTS was inaccurate.

I am unfamiliar with the Shearwater range and display's. However, I think I saw a sliding Stop Depth (as against a 3m incremental stops).
I am fully aware that most computers (and I assume the Shearwater), you can change the last stop depth. Obviously, if the last stop is at 3m (9ft), and you complete the last stop at 6m (18ft), the TTS will be inaccurate, as it is based on you moving too 3m.
However, I could swear that the ceiling was constantly moving, like the old 'dope on a rope' feature on the (very) old VR3's.

I would very much like to get a better understanding of the Petrel and how it behaves and the display, any information would be gratefully received.

Gareth

Sorry I am a little unclear on what your exact question is?

Your best bet to get a better understanding of how all Shearwater platforms behave is to just read the manufactures manual. https://www.shearwater.com/wp-content/uploads/2012/08/PetrelManual_DocRevD.pdf

But just to clarify some things you have mentioned the Petrel, Perdix, Teric, etc. all give stops in 3m incremented there is not moving stops. Once you clear the stop then it it will give you your next stop 3m up, etc. ect. and yes you can set the last stop depth. However the shearwater does give you a ceiling (not to be confused with your stop) and the ceiling is constantly moving up as you off gas. No the TTS is not inaccurate if you complete your last stop at 6m. If you clear your 6m stop and stay at 6m your TTS is still your TTS the computer recognizes that your at 6m and calculates your TTS based on the depth your at, just like if you were to hang out at 9m and not move up then your computers real time TTS display is based off of you being at 9m. However yes if you go into the dive plan and check your TTS (and you have your last stop at 3m in the settings) they it will assuming your making your last stop at 3m not 6m so the "plan" will be vary a slightly from what the actual TTS displayed on the computer is showing in real time.

If you are worried about computers not matching up then run the plan in multideco. I have found that multideco dive plans are pretty much spot on with what Shearwater computers give you. This will tell you all the stop times and total run time the Shearwater platforms will give you then you can adjust your dive plan accordingly

 

[Gareth J]

Sorry I am a little unclear on what your exact question is?

Your best bet to get a better understanding of how all Shearwater platforms behave is to just read the manufactures manual. https://www.shearwater.com/wp-content/uploads/2012/08/PetrelManual_DocRevD.pdf

But just to clarify some things you have mentioned the Petrel, Perdix, Teric, etc. all give stops in 3m incremented there is not moving stops. Once you clear the stop then it it will give you your next stop 3m up, etc. ect. and yes you can set the last stop depth. However the shearwater does give you a ceiling (not to be confused with your stop) and the ceiling is constantly moving up as you off gas. No the TTS is not inaccurate if you complete your last stop at 6m. If you clear your 6m stop and stay at 6m your TTS is still your TTS the computer recognizes that your at 6m and calculates your TTS based on the depth your at, just like if you were to hang out at 9m and not move up then your computers real time TTS display is based off of you being at 9m. However yes if you go into the dive plan and check your TTS (and you have your last stop at 3m in the settings) they it will assuming your making your last stop at 3m not 6m so the "plan" will be vary a slightly from what the actual TTS displayed on the computer is showing in real time.

If you are worried about computers not matching up then run the plan in multideco. I have found that multideco dive plans are pretty much spot on with what Shearwater computers give you. This will tell you all the stop times and total run time the Shearwater platforms will give you then you can adjust your dive plan accordingly

@marsh9077

Many thanks for the response.
I did have another quick look through the manual last night, and found the sliding ceiling reference. "Man on a rope", page 45 of the manual. This clarifies one of my observations.

Having scanned through the manual. It does state that if you choose to wait out the stop at 6m (when you have the option to move to 3m), then, the TTS is indicating the TTS from 6m to the surface. If you then move to 3m it will recalculate.
This is the first time I have seen this (to the best of my recollection). My usual experience is that the TTS is based on following the assumed set of stops, i.e. 1@9, 7@6, 15@3.
I like this feature, the majority of the stops I do are at 6m, (hence I normally have the 3m option turned off,) due to general sea conditions. It is nice to be able to move to 3m to speed up the decompression when conditions allow.

As an illustration. On one of my deeper dives, we chose not to switch to the decompression gas during the ascent, this threw the TTS calculation. Although you have to confirm the switch, the TTS is calculated on the basis that you will use the enabled decompression gas. Failing to switch to the decompression gas, means the TTS is misleading. However, if you haven't confirmed the switch once at (or above) the switch depth, the computer re-calculates on the basis that you are remaining on the last gas in use - so you get a new TTS.

However, this doesn't explain why our stops seemed to take longer than the initial TTS calculation, once we where at 6m.

 

[GF99/99]

@marsh9077

Many thanks for the response.
I did have another quick look through the manual last night, and found the sliding ceiling reference. "Man on a rope", page 45 of the manual. This clarifies one of my observations.

Having scanned through the manual. It does state that if you choose to wait out the stop at 6m (when you have the option to move to 3m), then, the TTS is indicating the TTS from 6m to the surface. If you then move to 3m it will recalculate.
This is the first time I have seen this (to the best of my recollection). My usual experience is that the TTS is based on following the assumed set of stops, i.e. 1@9, 7@6, 15@3.
I like this feature, the majority of the stops I do are at 6m, (hence I normally have the 3m option turned off,) due to general sea conditions. It is nice to be able to move to 3m to speed up the decompression when conditions allow.

As an illustration. On one of my deeper dives, we chose not to switch to the decompression gas during the ascent, this threw the TTS calculation. Although you have to confirm the switch, the TTS is calculated on the basis that you will use the enabled decompression gas. Failing to switch to the decompression gas, means the TTS is misleading. However, if you haven't confirmed the switch once at (or above) the switch depth, the computer re-calculates on the basis that you are remaining on the last gas in use - so you get a new TTS.

However, this doesn't explain why our stops seemed to take longer than the initial TTS calculation, once we where at 6m.

Yes that the TTS is always calculated based your current depth, gas, and runtime and will always recalculate if you change depth gas or time and also for the gases that are turned "on" in the settings. So if you have a bottom gas of 18/50 and then you have a 50% and 100% "on" then the computer is assuming you will make a switch to the 50% at 21m and 100% at 6m and the TTS is based off this. If you run this in multideco that plan will also match the Shearwater stop times and TTS. But if reach 21m and you do not switch to the 50% your gas display on the Shearwater will turn yellow indicated that there is a better gas available, same at 6m for the 100% however if your are not going to make the switch for some reason (maybe loss of gas) then you can turn the gas "off" and the computer will recalculate your new TTS based on that gas not being available.

If possible can you please list the stops and times that your computer gave and the stops and times your friends Shearwater gave so we can all see what the difference were and maybe help explain the discrepancy. Also what gases you used, when you switched etc.